JP4345179B2 - Magnetic field measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention applies a scanning probe microscope (SPM) technique to measure a local magnetic field near the surface of a magnetic recording medium, a magnetic film, etc. The present invention relates to a magnetic field measuring apparatus used for measurement.
[0002]
[Prior art]
For example, a magnetic force microscope (MFM) that has developed an atomic force microscope (AFM) technique as a means for measuring a local magnetic field near the surface of a magnetic recording medium or a magnetic film with high spatial resolution. Force Microscope) has been put into practical use.
[0003]
In a general magnetic force microscope, a magnetic chip provided at the free end of a cantilever is arranged near the surface of the sample, and the magnetic force acting on the magnetic chip is detected to detect a local magnetic field near the surface of the sample. However, it is assumed that a magnetic chip that has been previously magnetized is used.
[0004]
Therefore, in general magnetic force microscopes, in order to increase the detection sensitivity of the magnetic field, the cantilever is vibrated in the vicinity of the resonance frequency, and a change in amplitude and phase of the cantilever vibration is detected. However, in this case, the obtained result becomes a gradient image of the magnetic field and changes depending on the magnetization direction of the magnetic chip, so that there is a problem that it is difficult to interpret the measurement result.
[0005]
As a technique for solving such a problem, it is considered to control the magnetization of the magnetic chip, particularly to modulate it. As described above, when the method of modulating the magnetization of the magnetic chip is employed, the interaction between the magnetic field from the sample and the magnetic chip can be modulated, and an improvement in detection sensitivity of the magnetic field can be expected.
[0006]
For example, Applied Physics Letters, Volume 50 (1987), page 1455 and Japanese Patent Laid-Open No. 5-203626 are provided with an L-shaped magnetic cantilever having a tip as a probe. A magnetic field measuring device is disclosed in which a coil is wound near the base of a body cantilever and the current flowing through the coil is controlled to control the magnetization of the tip of the magnetic cantilever.
[0007]
Japanese Patent Application Laid-Open No. 11-108941 discloses a conductive chip having a magnetic chip formed at the free end of a cantilever and a coil portion on the magnetic chip forming surface of the cantilever where the base of the magnetic chip is positioned inside. There is disclosed a magnetic field measuring apparatus that controls the magnetization of a magnetic chip by forming a path and causing a current to flow through the conductive path to generate a magnetic field in the vicinity of the magnetic chip from the coil portion of the conductive path.
[0008]
[Problems to be solved by the invention]
However, like the magnetic field measuring device disclosed in Japanese Patent Laid-Open No. 5-203626, an L-shaped magnetic cantilever having a tip as a probe is provided, and a coil is wound around the base of the magnetic cantilever. In the configuration in which the magnetization of the tip portion is controlled by controlling the flowing current, there is a problem that the magnetization control of the tip portion cannot be performed efficiently.
[0009]
Further, in the configuration in which the coil part is formed at the base of the magnetic chip as in the magnetic field measuring device disclosed in Japanese Patent Application Laid-Open No. 11-108941, the magnetic field generated from the coil part is sampled even in parts other than the magnetic chip. In this case, the spatial resolution of the measurement is lowered.
[0010]
JP-A-11-166936 discloses a magnetic field measuring apparatus in which a coil is provided at the tip of a cantilever and the magnetic field generated by the coil is concentrated on the tip of the magnetic chip and does not leak to other parts. Is disclosed. According to this magnetic field measuring apparatus, although the spatial resolution can be improved, there is a problem that a very complicated process is required for processing the probe.
[0011]
In view of this point, the present invention can perform magnetic modulation of the magnetic chip provided at the free end of the cantilever with a simple configuration, and can measure a local magnetic field near the surface of the sample with high sensitivity. It is an object of the present invention to provide a magnetic field measuring apparatus that can be used.
[0012]
[Means for Solving the Problems]
The magnetic field measuring apparatus of the present invention has a magnetic tip capable of magnetization modulation at the free end of a cantilever, and a probe whose position relative to a sample can be relatively changed, and the bending of the cantilever inside the magnetic tip. it is arranged outside of the probe so as to be able to generate a magnetized direction, the magnetic material chip which is disposed in the vicinity of the surface of the sample, between the deflection direction of the end portion of the cantilever of the magnetic material chip a coil providing an alternating magnetic field spatial variation of the magnetic field of 1% or less, is that by supplying an alternating current to said coil has an AC power source for generating the alternating magnetic field.
[0013]
According to the present invention, an AC magnetic field can be applied to the magnetic chip disposed near the surface of the sample by the coil disposed outside the probe, so that the magnetic chip is caused to undergo magnetization modulation with a simple configuration. In addition, the interaction between the magnetic field generated by the coil and the magnetic field generated by the sample can be prevented from affecting the vibration of the cantilever. Further, since the coil gives the magnetic chip an alternating magnetic field in which the spatial change of the magnetic field between the ends of the cantilever of the magnetic chip is 1% or less, the magnetic field generated by the coil and the magnetic substance Cantilever vibration due to the interaction with the tip can be kept small.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a conceptual diagram of an embodiment of the present invention. In FIG. 1, 1 is a sample, 2 is a sample stage for holding the sample 1, 3 is a probe, and in the probe 3, 4 is a cantilever, 5 is a probe substrate for supporting the cantilever 4, and 6 is a free end of the cantilever 4. It is a magnetic chip made of a soft magnetic material that is provided on the lower side and is capable of magnetization modulation.
[0015]
Reference numeral 7 denotes a driving device having a moving mechanism of three or more axes and capable of driving the sample stage 2 or the probe 3 in three or more directions in order to change the relative position of the sample 1 and the probe 3. Sometimes, the magnetic chip 6 is operated so as to be positioned near the surface of the sample 1.
[0016]
Reference numeral 8 denotes a coil provided outside the probe 3 so that vertical magnetization can be generated inside the magnetic chip 6, and 9 denotes an AC power source for supplying an AC current to the coil 8. As described later, the inner diameter is sufficiently larger than the size of the magnetic chip 6 so that the spatial change of the magnetic field generated by the coil 8 in the vicinity of the magnetic chip 6 becomes very small. .
[0017]
Further, 10 is a deflection detector for detecting the vertical deflection of the free end of the cantilever 4, and 11 is for detecting a component synchronized with the alternating current output from the AC power supply 9 from the output signal of the deflection detector 10. Thus, the lock-in detector detects a local magnetic field in the vicinity of the surface of the sample 1.
[0018]
In one embodiment of the present invention, the magnetic chip 6 is positioned near the surface of the sample 1 by the driving device 7, an alternating current is supplied from the alternating current power source 9 to the coil 8, and the magnetic chip is generated by the alternating magnetic field generated by the coil 8. 6 is subjected to magnetization modulation, the magnetic force received by the magnetic chip 6 from the magnetic field generated by the sample 1 is periodically changed to vibrate the free end of the cantilever 4 in the vertical direction, and the vertical vibration of the cantilever 4 is detected by bending. The lock-in detector 11 detects a component that is detected by the detector 10 and that is synchronized with the AC current that is the output of the AC power supply 9 from the output signal of the deflection detector 10. It measures the magnetic field.
[0019]
In one embodiment of the present invention, the magnetic chip 6 is positioned in the vicinity of the surface of the sample 1 and, as is common in a scanning probe microscope, the magnetic chip 6 is not brought into contact with the sample surface and a certain amount. The step of scanning the magnetic chip 6 relative to the sample surface while being floated and measuring the magnetic field at each point is executed. The positioning of the magnetic chip 6 near the surface of the sample 1 is, for example, The sample table 2 or the probe 3 is driven by the driving device 7 to reduce the distance between the sample 1 and the magnetic chip 6, the tip of the magnetic chip 6 is brought into contact with the sample surface, and the magnetic chip 6 is detected by the deflection detector 10. It can be performed by detecting that the tip of the sample contacts the surface of the sample, and then increasing the distance between the sample 1 and the magnetic chip 6 by a certain amount.
[0020]
In one embodiment of the present invention, a substantially uniform magnetic field is generated in the vicinity of the magnetic chip 6 by the coil 8 having a sufficiently large inner diameter as compared with the size of the magnetic chip 6. 6 is subjected to magnetization modulation, and the modulation frequency f [Hz] is set in a range in which the magnetization of the magnetic chip 6 can sufficiently follow the AC magnetic field from the coil 8 and not more than the mechanical resonance frequency of the cantilever 4.
[0021]
FIG. 2 is a diagram for explaining the magnetization state of the magnetic chip 6 due to the alternating magnetic field generated by the coil 8. FIG. 2A shows the case where the direction of the alternating magnetic field 12 applied to the magnetic chip 6 is upward, and FIG. The case where the direction of the alternating magnetic field 12 given to the magnetic chip 6 is downward is shown.
[0022]
As shown in FIG. 2A, when the direction of the alternating magnetic field 12 applied to the magnetic chip 6 is upward, a positive magnetic charge 13 and a negative magnetic charge 14 are generated at the upper and lower ends of the magnetic chip 6, respectively. The magnetic chip 6 is magnetized as indicated by an arrow 15. In this case, for example, when an upward magnetic field 16 is applied from the sample 1, a downward magnetic force 17 is generated on the magnetic chip 6, and the cantilever 4 is moved downward. Will bend to the side.
[0023]
On the other hand, as shown in FIG. 2B, when the direction of the AC magnetic field 12 applied to the magnetic chip 6 is downward, the negative magnetic charge 18 and the positive magnetic charge are respectively provided at the upper end and the lower end of the magnetic chip 6. 19 is generated, and the magnetic chip 6 is magnetized as indicated by an arrow 20. In this case, for example, when an upward magnetic field 16 is applied from the sample 1, an upward magnetic force 21 is generated in the magnetic chip 6. The cantilever 4 is bent upward.
[0024]
In one embodiment of the present invention, the magnetic chip 6 is magnetically modulated by the alternating magnetic field 12 applied from the coil 8 so as to alternately take the magnetization state shown in FIG. 2A and the magnetization state shown in FIG. 2B. The magnetic force that the magnetic chip 6 receives from the magnetic field of the sample 1 changes at the frequency f, and the cantilever 4 vibrates at the frequency f. Therefore, in one embodiment of the present invention, the vertical deflection of the cantilever 4 is detected by the deflection detector 10 and the amplitude and phase of the vertical vibration of the cantilever 4 is detected by the lock-in detector 11. Yes.
[0025]
Here, since the amplitude of the vertical vibration of the cantilever 4 is proportional to the magnitude of the component perpendicular to the sample surface of the magnetic field in the vicinity of the surface of the sample 1 where the sample 1 is generated, the surface of the sample 1 where the sample 1 is generated The magnitude of the nearby vertical magnetic field can be determined by detecting the amplitude of the vertical vibration of the cantilever 4.
[0026]
2A, the cantilever 4 bends downward when the alternating magnetic field 12 is upward, or the cantilever 4 bends upward when the alternating magnetic field is downward as shown in FIG. 2B. If there is, it can be seen that the magnetic field of the sample 1 is upward, and the phase relationship that the cantilever 4 bends upward when the alternating magnetic field is upward, or the phase relationship that the cantilever 4 bends downward when the alternating magnetic field is downward. If there is, it can be seen that the magnetic field of the sample 1 is downward.
[0027]
In the example of FIG. 2, the magnetic force received by the magnetic chip 6 is received by the surface magnetic charges 14 and 19 at the lower end of the magnetic chip 6. This is because the magnetic force received by the magnetic chip 6 from the sample 1 is divided into the magnetic force received by the surface magnetic charges 14 and 19 at the lower end of the magnetic chip 6 and the magnetic force received by the upper surface magnetic charges 13 and 18. Since the upper end of the magnetic chip 6 is far from the surface of the sample 1, the magnetic field from the sample 1 is weakened and the magnetic field from a wide portion of the surface of the sample 1 is averaged, so that it has a fine structure. In this case, since they are averaged, it can be considered that the magnetic force received by the surface magnetic charges 14 and 19 at the lower end of the magnetic chip 6 is dominant, and the magnetic force received by the magnetic chip 6 is There is no problem even if the surface magnetic charges 14 and 19 at the lower end of the magnetic chip 6 receive.
[0028]
Thus, in one embodiment of the present invention, the vibration of the cantilever 4 synchronized with the magnetic field modulation is detected, so that the cantilever 4 is vibrated by the AC magnetic field 12 from the coil 8 regardless of the magnetic field from the sample 1. Must be avoided. Therefore, the inner diameter of the coil 8 is increased, and the spatial change of the magnetic field due to the coil 8 in the size of the magnetic chip 6 is reduced. This is because as the spatial change is smaller, the magnetic force received by the magnetic chip 6 by the magnetic field of the coil 8 decreases.
[0029]
Therefore, the degree to which the spatial uniformity of the magnetic field generated by the coil 8 is necessary will be considered. The magnetization of the magnetic chip 6 is caused by the magnetic field from the coil 8, the magnetic force due to the magnetic field from the sample 1 acts on the magnetization m at the lower end, and the magnetic force on the magnetization -m at the upper end is ignored as described above. The magnetic force generated by the magnetic field from the coil 8 works so as to cancel the magnetic charge m at the lower end and the magnetic charge −m at the upper end, but it remains without being canceled by a spatial change.
[0030]
Considering the case where a magnetic field of 1 mT is applied from the coil 8 to the magnetic chip 6 and the magnetic field of the sample 1 of 0.01 mT is measured, the magnetic force due to the magnetic field from the sample 1 is mx 0.01. Since the magnetic force due to the magnetic field from the coil 8 is m × 1 × space change rate, in order for these two to be comparable, the change in the magnetic field of the coil 8 at the upper and lower ends of the magnetic chip 6 The amount must be 1% or less.
[0031]
For example, assuming that the length of the coil 8 is 2 mm, the distance between the lower end position of the magnetic chip 6 and the upper end of the coil 8 is 1 mm, and the size of the magnetic chip 6 is 50 μm in the axial direction of the coil 8. If the inner diameter of the coil 8 is 10 mm or more, the spatial change of the magnetic field from the coil 8 is 1% or less. That is, the inner diameter of the coil 8 needs to be 200 times or more the size of the magnetic chip 6, particularly the length in the magnetization direction.
[0032]
In addition, since the magnetic force by the magnetic field from the coil 8 acts on what is magnetized by itself, when the magnetic field from the coil 8 is reversed, the magnetization of the magnetic chip 6 is also reversed. Therefore, the vibration frequency of the cantilever 4 is an AC magnetic field. Twice the frequency (2f). Therefore, even if there is a vibration equivalent to the vibration (frequency f) due to the magnetic field from the sample 1, the influence is reduced by detecting lock-in, and the vibration due to the magnetic field from the sample 1 can be measured with high accuracy. it can.
[0033]
In the above description, the vibration of the cantilever 4 having the frequency 2f that is vibrated by the magnetic field from the coil 8 has been considered. However, the vibration having the frequency f caused by the residual magnetization of the magnetic chip 6 is also considered as an influence on the measurement. There is something. Although it is called residual magnetization, it may be considered that the magnetic chip 6 is magnetized by a magnetic field existing in the environment such as geomagnetism. If such residual magnetization exists in the magnetic chip 6, when an AC magnetic field is applied by the coil 8, a slight but spatially changing magnetic field from the coil 8 acts on the residual magnetization, and the cantilever 4 has a frequency f. Vibration will occur.
[0034]
In order to suppress the vibration of the cantilever 4 due to such residual magnetization, as shown in FIG. 3, a DC power source 22 that outputs a DC current with a variable current value is provided, and a DC current is supplied from the DC power source 22 to the coil 8. It is effective to supply a current and generate a DC magnetic field. This is because the residual magnetization can be canceled by such a DC magnetic field.
[0035]
Specifically, the magnetic chip 6 is moved to a position where the magnetic field from the sample 1 does not exist, the alternating current from the alternating current power source 9 and the direct current from the direct current power source 22 are supplied to the coil 8 to detect lock-in. The value of the direct current output from the direct current power source 22 is adjusted and fixed so that the value is close to zero, that is, the vibration of the cantilever 4 is minimized.
[0036]
The embodiment of the present invention can be used not only when measuring a local magnetic field in the vicinity of the surface of a magnetic recording medium or a magnetic film, but also when measuring a current of a minute wiring of an integrated circuit. . FIG. 4 is a diagram for explaining a method of measuring a current flowing through a wiring of an integrated circuit using one embodiment of the present invention. In FIG. 4, 23 is an integrated circuit, and 24 is a wiring.
[0037]
When the current flowing through the wiring 24 of the integrated circuit 23 is measured using the embodiment of the present invention, the magnetic chip 6 is scanned across the wiring 24 above the wiring 24 and the current flowing through the wiring 24 is measured. The lock-in detection value is measured by detecting the magnetic field generated by. In this way, for example, a graph as shown in FIG. 5 can be obtained. The vertical axis indicates the detected magnetic field intensity, and is expressed as negative when the phase is inverted. Further, the horizontal axis indicates the position of the magnetic chip 6 in the scanning direction, and it can be seen that the wiring 24 is located near the zero detected magnetic field intensity on the line crossing the wiring 24. Since it has been confirmed that the change amount 25 of the magnetic field intensity shown in the figure is proportional to the current value of the wiring 24, the current value of the wiring 24 can be calculated from the change amount 25.
[0038]
FIG. 6 is a view showing a first specific example of one embodiment of the present invention, in which the shape of the coil 8 and the sample position 26 are shown, and the other portions are not shown. In this example, the coil 8 has an inner diameter of 50 mm and a length of 10 mm, and the sample position 26 is located on the axis of the coil 8 at a distance of 15 mm from the end of the coil 8. In this way, the spatial change of the alternating magnetic field at a position 10 μm apart on the axis at the sample position 26 can be reduced to 0.1% or less, which is suitable when a magnetic chip 6 having a size of about 10 μm is used. It will be.
[0039]
In order to further reduce the spatial change of the alternating magnetic field generated by the coil 8, it is advantageous to set the sample position 26 near the center inside the coil 8. However, if the sample position 26 is set inside the coil 8, Since the size of the sample 1 is limited, in one embodiment of the present invention, the sample position 26 is outside the coil 8. In addition, the inner diameter of the coil 8 is very large, 5000 times the size of the magnetic chip 6, but this is not only for spatial uniformity, but also for applying a magnetic field to a position about 15 mm away with a small current. This is because a larger coil 8 is more suitable.
[0040]
FIG. 7 is a diagram showing a second specific example of one embodiment of the present invention. In the second specific example of one embodiment of the present invention, the sample stage 2 is made of a nonmagnetic material having a low magnetic permeability. Used, the coil 8 is arranged at the lower part of the sample stage 2. Further, a triaxial stage 27 using a piezo element is used as the driving device 7, and the probe 3 is fixed to the tip of the triaxial stage 27 so that it can move in the triaxial direction with respect to the sample 1. ing.
[0041]
In addition, the deflection detector 10 includes a semiconductor laser 28 and a two-divided light receiver 29 in order to use the principle of optical lever, and the reflected light of the laser light irradiated to the cantilever 4 from the semiconductor laser 28 is 2 It is assumed that the position of the reflected light received by the split light receiver 29 and reflected on the split light receiver 29 is output. Reference numeral 30 denotes a support, and the coil 8 and the column 31 of the sample table 2 are fixed to the support 30. The lock-in detector 11 and the AC power source 9 are not shown.
[0042]
FIG. 8 is a diagram showing a third specific example of an embodiment of the present invention. In FIG. 8, reference numeral 32 denotes a triaxial stage using a piezo element forming the driving device 7, the sample stage 2 is on the triaxial stage 32, and the triaxial stage 32 is fixed to the support 33. . The coil 8 is disposed above the sample 1 and is fixed to the support 33 via the fixing portion 34, and the probe 3 is fixed to the tip of the support 33 that penetrates the inside of the coil 8. Yes. The deflection detector 10, the lock-in detector 11, the AC power source 9, and the like are not shown.
[0043]
As described above, according to an embodiment of the present invention, an AC magnetic field can be applied to the magnetic chip 6 disposed near the surface of the sample 1 by the coil 8 disposed outside the probe 3. The magnetic chip 6 formed at the free end of the cantilever 4 can be subjected to magnetization modulation with a simple configuration, and the interaction between the magnetic field generated by the coil 8 and the magnetic field generated by the sample 1 is the vibration of the cantilever 4. Can be prevented from affecting anything. Further, since the spatial change in the vicinity of the magnetic chip 6 of the AC magnetic field by the coil 8 is made small, the vibration of the cantilever 4 due to the interaction between the AC magnetic field generated by the coil 8 and the magnetic chip 6 should be ignored. Can be made as small as possible.
[0044]
Therefore, the magnetic modulation of the magnetic chip 6 provided at the free end of the cantilever 4 can be performed with a simple configuration without preparing a probe having a complicated configuration as provided in the magnetic field measuring apparatus disclosed in Japanese Patent Application Laid-Open No. 11-166936. Moreover, local magnetic field measurement in the vicinity of the surface of the sample 1 can be performed with high sensitivity.
[0045]
Incidentally, a probe microscope disclosed in Japanese Patent Application Laid-Open No. 11-142105 is similar to the present invention. Although this probe microscope is not intended for magnetic field measurement, it is described that the probe microscope includes a cantilever having a magnetic chip and a coil arranged outside the probe, and an alternating current flows through the coil. However, this probe microscope uses a coil to vibrate the cantilever positively, contrary to the present invention, and the shape is also suitable for it, that is, the spatial change near the magnetic chip is greatly increased. This is to be done and is essentially different from the present invention.
[0046]
【The invention's effect】
As described above, according to the present invention, the coil disposed outside the probe can be configured to apply an alternating magnetic field with small spatial change to the magnetic chip disposed near the surface of the sample. Magnetization modulation can be caused with a simple configuration on the magnetic chip formed at the free end of the cantilever, and a local magnetic field in the vicinity of the surface of the sample can be measured with high sensitivity.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an embodiment of the present invention.
FIG. 2 is a diagram for explaining a magnetization state of a magnetic chip by an alternating magnetic field generated by a coil in an embodiment of the present invention.
FIG. 3 is a diagram showing a modification of one embodiment of the present invention.
FIG. 4 is a diagram for explaining a method for measuring a current flowing through a wiring of an integrated circuit using an embodiment of the present invention.
FIG. 5 is a diagram for explaining a method of measuring a current flowing through a wiring of an integrated circuit using an embodiment of the present invention.
FIG. 6 is a diagram showing a first specific example of an embodiment of the present invention.
FIG. 7 is a diagram showing a second specific example of an embodiment of the present invention.
FIG. 8 is a diagram showing a third specific example of an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sample 2 Sample stand 3 Probe 4 Cantilever 5 Probe board 6 Magnetic chip 7 Driving device 8 Coil 9 AC power supply 10 Deflection detector 11 Lock-in detector 12 AC magnetic field 13 Positive magnetic charge 14 Negative magnetic charge 15 Direction of magnetization 16 Magnetic field 17 Magnetic force 18 Negative magnetic charge 19 Positive magnetic charge 20 Direction of magnetization 21 Magnetic force 22 DC power supply 23 Integrated circuit 24 Wiring 25 Magnetic field strength change 26 Sample position 27 Triaxial stage 28 Semiconductor laser 29 Two-divided light receiver 30 Support 31 support 32 triaxial stage 33 support 34 fixing part

Claims (2)

A probe having a magnetic material chip that can modulate magnetization at the free end of the cantilever, and the position of the probe relative to the sample can be changed relatively;
The magnetic chip is arranged outside the probe so that magnetization can be generated in the bending direction of the cantilever inside the magnetic chip, and the magnetic chip is arranged near the surface of the sample . A coil for applying an alternating magnetic field in which the spatial change of the magnetic field between the ends in the bending direction of the cantilever is 1% or less ;
A magnetic field measuring apparatus having an AC power source for supplying an AC current to the coil to generate the AC magnetic field.   The magnetic field measuring apparatus according to claim 1, further comprising a DC power source that supplies a DC current whose current value is variable to the coil.

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